It looks like his changes appear in the game window without rebuilding the program. Is that what everyone else is seeing? Is this a technique I should know about?
Hotswap bug fixing is the Java term for it. .NET calls it Edit and Continue. Much the same thing has existed in Smalltalk and Lisp etc. for much longer.
It's particularly well suited for things like a game loop or a server, because it works best (or rather usually, only) when the code you're editing is not on the stack.
Are you still limited to method bodies? It seems reasonable that the method signatures and object layouts couldn't be modified because that would invalidate a lot of code already in memory and that may already be optimized.
It's particularly well suited for things like a game loop or a server, because it works best (or rather usually, only) when the code you're editing is not on the stack.